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DeepSpace
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 Posted: Mar 28, 2004 - 03:52 AM
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Elite 1K
Joined: Aug 14, 2003 - 07:26 PM
Posts: 1050
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Hi.
I've just heard that early F-16's flight computers were having problems when flying below an altitude of 0, and their engines were being shut down.
Is that rumor correct?  |
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 Posted: May 26, 2012 - 2:21 PM
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F-16.net Sponsor
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habu2
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Posted: Mar 28, 2004 - 05:11 AM
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Elite 2K
Joined: Sep 05, 2003 - 09:36 PM
Posts: 2812
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I've never heard of such a rumor, and see no reason why it would even be a factor.
While early F-16s were "fly-by-wire" they were not digital systems - the flight control computers were still analog.
To my knowledge there are only two places on earth you could even attempt flying below sea level (assuming that is what you meant) - Death Valley in the western US and the Dead Sea in the Middle East. |
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Reality Is For People Who Can't Handle Simulation
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DeepSpace
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Posted: Mar 28, 2004 - 06:17 AM
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Elite 1K
Joined: Aug 14, 2003 - 07:26 PM
Posts: 1050
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| Yes, Habu2, I meant below sea level. And such a thing was important (it's more than a rumor) because of the Dead Sea which is on the Jordanian/Israeli border. |
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DeepSpace
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Posted: Mar 28, 2004 - 12:24 PM
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Elite 1K
Joined: Aug 14, 2003 - 07:26 PM
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Ok, I got the information. The first time they discovered the problem was during a flight in the Death Valley. While the aircraft was below see level, the flight computer was given the altitude of 0 and tried to divide by 0. Because of that the fire control system and some others crashed.
The second time it happened was in the Dead Sea, with the IAF. In this incident the pilot changed the FBW system (that was analog that time) into manual mode, and landed the plane in the nearest AB. That's all I knew about these two incidents.
Notice that in both of the cases nothing happened to the aircrafts' engine. |
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habu2
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Posted: Mar 28, 2004 - 05:11 PM
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Elite 2K
Joined: Sep 05, 2003 - 09:36 PM
Posts: 2812
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| We encountered this problem (negative altitude) in the F-15E flight sim, but not in the flight control system - it was in the simulation of the radar altimeter. |
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Reality Is For People Who Can't Handle Simulation
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yamatosam
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Posted: Mar 28, 2004 - 05:59 PM
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Newbie
Joined: Jan 18, 2004 - 05:55 AM
Posts: 19
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| If your landing at NAF El Centro in tthe Imperial Valley, Ca your landing below sea level. |
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Gums
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Posted: Mar 29, 2004 - 07:08 AM
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Elite 1K
Joined: Dec 16, 2003 - 05:26 PM
Posts: 1242
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No no no!
The Air Data system used mach and such for LEF's. The basic FLCS used mach, air density and dynamic pressure for 'gains'.
Even with digital system, no division by zero problem. 'Pure' altitude not used, as stated above.
urban legend,
out, |
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Gums
Viper pilot '79
"God in your guts, good men at your back, wings that stay on - and Tally Ho!"
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habu2
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Posted: Mar 29, 2004 - 04:32 PM
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Elite 2K
Joined: Sep 05, 2003 - 09:36 PM
Posts: 2812
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I still don't see (a) how this would be a problem and (b) how the aircraft would know it was below sea level.
If you set your barometric altimeter for sea level, going below sea level would only be seen as a (minimally) higher barometric pressure and displayed as such on an analog instrument.
In the case of a radar altimeter, the radar return is always AGL - no matter what the elevation of ground level is.
As Gums implied, the FLCS gets its inputs from the air data system. |
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Reality Is For People Who Can't Handle Simulation
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habu2
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Posted: Mar 29, 2004 - 04:51 PM
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Elite 2K
Joined: Sep 05, 2003 - 09:36 PM
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Quote:
The first time they discovered the problem was during a flight in the Death Valley. While the aircraft was below see level, the flight computer was given the altitude of 0 and tried to divide by 0. Because of that the fire control system and some others crashed.
Badwater Basin in Death Valley has an elevation of -279 ft - and that is the lowest point. The average over the valley seems to be about -200. (see topographic map here: http://www.death.valley.national-park.com/map.htm) Given the geographic constraints (length and width) of the valley I don't see how or why any flight testing would have been done here.
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The second time it happened was in the Dead Sea, with the IAF.
The surface of the Dead Sea is at about -1300 ft (see topographic map here: http://pubs.usgs.gov/of/of01-216/imgs/deadsea.gif) so there is a greater chance to "fly below sea level" but I won't ask why Israeli jets were flying low level along the Jordanian border in this forum... |
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Reality Is For People Who Can't Handle Simulation
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Gums
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Posted: Mar 29, 2004 - 05:18 PM
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Elite 1K
Joined: Dec 16, 2003 - 05:26 PM
Posts: 1242
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Salute!
One mo' time!!!!!
I am holding the FLCS design manual in my gnarled, stiff fingers.
The FLCS does not use the 'altimeter' setting. It uses dynamic pressure and static pressure and mach.
It is possible to have static pressure equal to or below 'standard' mean sea level when flying above 1000 feet if it is really cold outside. So sea level is not a player.
The autopilot does not use the FLCS air data, it uses the same data that is displayed on the altimeter and airspeed indicator. It uses the change in altitude from when it is engaged, and is not referenced to sea level. So I rule out an autopilot problem. Besides, anyone using autopilot at low altitude is crazy.
I have also personally witnessed the FLCS react to zero/negative airspeed. Vertical climb, looking over shoulder, speed decays, Gums keeps heading vertical, Viper does a tailslide (heh heh). All FLCS lights come on as angle-of-attack probes go awry and speed becomes negative. Nose falls thru and within2-3 seconds I am flying O.K. reset FLCS caution/warning lights and continue the fight.
out, |
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Gums
Viper pilot '79
"God in your guts, good men at your back, wings that stay on - and Tally Ho!"
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habu2
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Posted: Mar 29, 2004 - 06:44 PM
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Elite 2K
Joined: Sep 05, 2003 - 09:36 PM
Posts: 2812
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I agree w/Gums, you might get warning lights (after all that is what they are for) but I don't see the FLCS 'crashing' or causing engine shut downs...
I've seen videos of the XL doing tailslides too - very interesting. |
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Reality Is For People Who Can't Handle Simulation
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Cylon
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Posted: Apr 03, 2004 - 03:20 AM
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Senior member
Joined: Dec 09, 2003 - 01:16 AM
Posts: 341
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Gums is correct. (no sh*t, agree with the old guy.. SUPRISE....)
Now, if you roll inverted and valsalva twice.... The FLCS will command ejection.
Cylon |
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elp
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Posted: Apr 05, 2004 - 03:55 PM
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F-16.net Editor
Joined: Sep 23, 2003 - 09:08 PM
Posts: 3133
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Cylon wrote:
Now, if you roll inverted and valsalva twice.... The FLCS will command ejection.
Cylon
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habu2
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Posted: Apr 05, 2004 - 05:14 PM
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Elite 2K
Joined: Sep 05, 2003 - 09:36 PM
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